Heidrick Consulting net revenue decreased 1.0%, or $0.2 million, to $15.5 million from $15.7 million in the 2017 third quarter. The decline largely reflects the impact of the new revenue recognition accounting on enterprise license agreements, which increased deferred revenue thereby reducing net revenue in the quarter by approximately $0.9 million. There were 30 Heidrick Consulting Partners at September 30, 2018 compared to 27 at September 30, 2017 and 31 at June 30, 2018.
Consolidated salaries and employee benefits expense in the 2018 third quarter increased 23.4%, or $25.4 million,to $133.9 million from $108.5 million in the 2017 third quarter. Fixed compensation expense increased $9.3 million largely reflecting higher costs for talent acquisition and retention. Variable compensation expense increased $16.1 million, primarily reflecting higher bonus accruals for Executive Search consultant performance. Salaries and employee benefits expense was 71.4% of net revenue for the quarter compared to 67.9% in the 2017 third quarter.
General and administrative expenses declined 11.2%, or $4.2 million, to $33.1 million from$37.2 million in the 2017 third quarter. Savings were achieved in a number of expense categories, but lower internal travel expense, a reduction in the use of external third-party consultants, lower IT communications costs, and lower bad debt expense were the primary drivers of the decline in G&A expense. As a percentage of net revenue, general and administrative expenses were 17.6% compared to 23.3% in the 2017 third quarter.
Operating income in the 2018 third quarter increased 46.8%, or $6.6 million, to $20.6 million from $14.0 million in the 2017 third quarter. The operating margin (operating income as a percentage of net revenue) improved to 11.0% compared to operating margin of 8.8% in the same quarter of 2017. Adjusted EBITDA in the 2018 third quarter increased $8.5 million to $26.4 million from $18.0 million in the 2017 third quarter. The Adjusted EBITDA margin(Adjusted EBITDA as a percentage of net revenue) in the 2018 third quarter was 14.1% compared to 11.2% in the 2017 third quarter. The improvements in operating income and Adjusted EBITDA were primarily driven by the increase in revenue from Executive Search.
In the 2018 third quarter, net income more than doubled to $16.5 million and diluted earnings per share was $0.85 with an effective tax rate of 29.0% in the quarter and a full-year projected tax rate in the low 30% range. This compares to net income of $8.2 million in the 2017 third quarter and diluted earnings per share of $0.43, with an effective tax rate of 42.7%.
Net cash provided by operating activities in the 2018 third quarter was $84.2 million,compared to $50.2 million in the 2017 third quarter. Cash and cash equivalents at September 30, 2018 were $164.2 million compared to $207.5 million at December 31, 2017, and $105.7 million at September 30, 2017.
Nine Months Results
For the nine months ended September 30, 2018 consolidated net revenue of $530.7 million increased 17.4%, or $78.7 million, from $452.0 million in the first nine months of 2017. Excluding the impact of exchange rate fluctuations which positively impacted results by $6.5 million, or 1.2%, consolidated net revenue increased 16.0% or $72.2 million. The company’s adoption of ASC 606 on January 1, 2018, increased consolidated net revenue in the first nine months of 2018 by $1.3 million compared to the historical method of revenue recognition.
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